The present invention relates to a method of addition of polymerization initiator and, in more detail, to a charging method of polymerization initiator capable of charging low-temperature-active polymerization initiator into polymerization system at ordinary temperature.
In the so-called suspension polymerization wherein a polymerizable monomer, for example, vinyl chloride monomer is polymerized by the use of aqueous medium, low-temperature-active organic peroxides or azo-bis compounds are used as initiators for polymerization reaction.
Recent trends of manufacturing process are as follows:
1) Polymerization is performed in a closed system using antifouling agent or the like. This is for omitting the conventional procedure of opening manhole every batch for the removal of scale, for preventing the escape of gas remaining in the reactor, for avoiding the problems of labor and common environment, and further for shortening the time of one cycle to improve the productivity and reduce the cost. PA1 2) Uniform development of heat of reaction has been sought for shortening the reaction time and improving the productivity because it permits easy heat removal and easy control of reaction as well, and initiators which are more active at low temperature have come to be used most frequently. That is, a plurality of initiator types having appropriate characteristics to reaction temperature have come to be selected for use in combination as if they were starting, relay and relief pitchers in ball game. PA1 3) Organic peroxide initiators have some water solubility. Thus, when they are added beforehand to an aqueous phase and thereafter monomer is added to polymerize, the polymerization product in aqueous phase becomes bead-like nonporous particles to increase the fish-eye characteristic of final product. It is necessary therefore to charge these peroxide initiators into monomer phase. PA1 1) Double-pipe, cooling equipment and refrigerant-circulating equipment are required, thus, in the case of having many polymerization reactors or permitting several types of initiators to be charged at an arbitrary rate, considerable capital investment is required, PA1 2) The initiators are present in the piping system at all times, thus maintenance and management costs such as power etc. are required for cooling, and PA1 3) If the temperature of the initiator rises due to accidents such as power failure etc., the decomposition begins resulting in the dangers of explosion and fire in extreme cases, thus, in such cases, there is troublesome work such as draining of contents, and washing which are required (it is not preferable to have potentially dangerous factors in a plant).
Moreover, all of these initiators decompose more or less depending on their types. Hence, it is necessary to retain them at a low temperature lower than 5.degree. C. for preventing the decomposition.
Based on these reasons, a method is taken for charging initiators such that the initiators retained at low temperature are metered immediately before charging and charged into a closed polymerization reactor by throwing them at once into an equalizing charger or charged with a booster pump, but it does not match to the modern times because of taking time and insufficient charge accuracy. Moreover, the conventional automatic charging method of initiator uses a double-pipe system (i.e., a pipe arrangement having an inner pipe and an outer pipe in a concentric relationship), and the outside is retained at low temperature by passing refrigerant of 5 to -20.degree. C., thus performing the metered charging.
The method disclosed in Japanese Unexamined Patent Publication No. Sho 63-41507 is a pioneering work to the invention, which teaches the simultaneous addition of initiator to a water slurry of various powdery additives to be added for polymerization reaction. This is not practical however as a charging method of initiator, since the initiator is adsorbed onto various additives and exerts interactions.
When charging initiator into a polymerization system by the conventional method using a double-pipe system,
As described above, the charging method of prior art has unpreferable problems. As a result of diligent investigations, the inventors have found a method solving these problems at a stroke, leading to the completion of the invention.